Unit 3

Intro to the Skeletal System

The different parts of the skeletal system are: Bone( extracellular matrix- collagen and minerals, flexible), Joints, Cartilage( extracellular matrix- cartilage and proteoglycans), Tendons and Ligaments( tough collagen)

The skeleton is divided into two divisions: Axial and Appendicular Skeleton

Bone Functions

  • support body

  • protect organs in body

  • movement

  • storage of minerals and fats

  • Blood cell formation

Bones in Human Body

  • 206 bones(adult)

  • 2 types of bone tissue

    • compact

      • outer part of diaphysis (long bone) and thinner surface of other bones

      • osteon: structural unit of compact

    • Spongy bone

      • open spaces

      • location: epiphyses of long bones and center of other bones

      • no osteons

Types of Bone

  • Long Bone

    • shaft at both ends

    • contains mostly compact bone

    • Femur, humerus

  • Short Bone

    • cube shape

    • mostly spongy bone

    • carpals, tarsals

  • Flat Bone

    • thin and flat

    • thin layer of compact around a large layer of spongy bone

    • skull, rib, sternum

  • Irregular Bone

    • not in other bone classification categories

    • vertebrae/ hip


A Closer Look at At Bones

  • osteoprogenitor cells=stem cells

  • osteoblasts= build bone

  • osteocytes= maintain bone matrix(from osteoblasts)

  • osteoclasts= break down bone to release Ca and Phosphate; respond to forces placed on bone

Microscopic Anatomy of Bone

  • osteon —> a unit of bone

  • Central (Haversian) Canal: opening in the center of a osteon, carries blood vessels and nerves

  • perforating(volkman) canal: perpendicular to central canal, carries blood vessels and nerves

  • Lacunae: cavities containing bone cells(osteocytes), rings

  • Lamellae: rings around central canal, lacunae sites

  • Canaliculi: Tiny canals, from central canal to lacunae, transport system

Bone Formation

  • ossification= bone formation, in utero

    • Osteoblast role

      • builds bone

      • after osteoblast becomes surrounded by bone matrix becomes osteocyte

  • ossification begins in embryo and continues as skeleton grows(even as adults)

  • after 8-12 weeks of embryonic dev skeleton forms through thick cartilage which are soon replaced by hard bone

    • ossification center-bone formation begins

    • primary- bone 1st begins to appear(diaphysis)

    • second- forms epiphyses

  • Steps:

    • chondroblasts build cartilage model and become chondrocytes

    • cartilage hardens

    • osteoblasts invade calcified cartilage and form diaphysis(primary)

    • secondary form epiphyses

Bone Growth

  • long bones lengthen at epiphyseal plate

  • widen by more lamella

  • bone growth ends when epiphyseal plate is replaced by a line


    Remodeling

  • osteoclasts remove and osteoblasts give new bone

  • responsible for changes in bone shape

  • they adjust to stress and calcium ion regulation

Repair

  • broken bone=bleeding=blood clot=callus(fibrous network between 2 fragments)

  • cartilage model forms→ osteoblasts enter→ cancellous bone (4-6 weeks)

  • cancellous bone is remodeled to form compact and cancellous bone

Bone/Calcium Homeostasis

  • calcium is stored in bone, and movement in and out of bone helps determine blood levels of calcium

    • into= osteoclasts build

    • out=osteoblasts break

    • homeostasis maintained by parathoid hormone and calcitonin

Hematopoietic Tissue

  • makes red blood cells (red marrow)

  • yellow marrow: fat

  • newborns?

    • red marrow

  • adults?

    • red is replaced with yellow marrow, red marrow is in femur/humerus and axial skeleton’